Does a 3.7V Lithium Battery Charge Automatically When USB is Connected, and What Current Does the USB Type-C Input Support?

#1

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Title: Does a 3.7V Lithium Battery Charge Automatically When USB is Connected, and What Current Does the USB Type-C Input Support?

Message:

Hello everyone,

I am working with a system that uses a 3.7V lithium battery connected via a JST port and a USB Type-C input. I have a few questions and hope someone with experience can help clarify them:

  1. Does the battery charge automatically when the USB input is connected?
  • I would like to know if connecting the USB input to the device automatically charges the lithium battery through the JST port interface or if any additional steps are required.
  1. Is it possible to connect an external charger to the USB Type-C input?
  • I would like to confirm whether I can use an external charger connected to the USB Type-C input and if it is safe for charging the battery.
  1. What is the maximum current allowed by the USB Type-C input?
  • I want to know the maximum current that the USB Type-C input can handle to avoid overloading and potential damage to the system.

I appreciate any advice or experiences you can share on this topic.

Thank you for your help!

#2

Yes, after connecting both the USB and lithium battery to the development board, the lithium battery can be charged directly.

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#3

For a more detailed reply, tell us the actual device model!

For a self-help reply, look at the schematic for the device and then lookup the charging chip specs!

For a reality check, going wrong with LiPo is very rarely catastrophic, but you should be diligent in your own research because any mishaps are on you!

#4

Wireless Stick Lite V3

#5

That is sound advice :slight_smile:
Sorry to hijack the thread.
I have a Heltec WiFi LoRa 32 (V3.2) board with OLED and I notice the charging circuit, the ESP32 and the LoRa chip all get extremely hot when I connect a battery and plugged in to USB.
By extremely hot I mean it burns you when touched.

I have 3 Heltec boards (all same type) and 4 batteries (3.7V, 3000mAh by MakerFocus) and they all behave the same.

Do you know if this is normal and is there a workaround? It would be great if the charging rate can be throttled. I’m also a bit cautious of the fire hazard.
Thanks.

#6

This is exceptionally bad and the workaround is to unplug it all and start again with far more detail so we can figure out what you’ve done.

Why? How is this relevant?

Perhaps not cautious enough if you tried all four batteries. Have you seen a LiPo fire? Almost impossible to put out. Hot as hell. Poisonous fumes. Can cope for hours and then spontaneously alight.

As lots of us use the LiPo circuit, either you have a faulty board or more likely, have not checked the polarity of the battery you plugged in.

#7

The LiPo battery isn’t getting hot so I’m not too concerned about the battery catching fire. Infact it stays cool. It is the Heltec board, specifically the charging circuit, the ESP32 processor and the LoRa chip which gets extremely hot.

The polarity is ok. The Heltec board runs fine just off the battery (without the USB plugged in). It is when the USB is plugged in (and hence charging the battery) that the board heats up. Battery stays cool all the time.

I have nothing else connected to the Heltec board, except the Lora antenna, the USB cable from my laptop or power bank, and the LiPo battery.

And I have tried it with all my 3 Heltec boards, and 4 batteries - all the same behaviour.

Not really sure how to troubleshoot this one.

#8

You win the “additional relevant details award” for 2025!

Oh Kay. What if something on the board finally fails and then …

I’d certainly not leave this kit plugged in unattended.

Look at the power flow in the schematic.

Something is getting super hot and probably transferring the heat to the other components. Find the hottest item and tell us what it is and we can all look see how that is involved in the power circuitry.

#9

I did some more testing and found some interesting things. This time I uploaded a minimal sketch which only reads the battery voltage and displays it on the OLED. So minimal load on the ESP32 and no load on the SX1262. The components getting hot are shown in orange and red squares.

I couldn’t find a drawing showing all the components. Some components are a question mark.

With the battery connected, and USB connected, the battery voltage was recorded as follows:
t=0h 3.45V
t=1h 3.51V
t=2h 3.60V
t=3h 3.73V
t=4h 3.86V
This was as high as the voltage got.
The chip next to the yellow LED remained hot but the other components started to cool down at 3.6V. This matches what someone else posted; the charge rate is inversely proportional to the batter voltage.

When I disconnected the USB the battery voltage dropped from 3.86V to 3.77V.

2%20Battery%20Charging%20Hot%20Components
Heltec LoRa V3.2 Battery Charging Hot Components.jpg1024×713 146 KB

The battery stayed cool the whole time.
Last time I saw the high temps I had a sketch containing quite a load on the ESP32 and the SX1262 and noticed temperatures were higher than this time. Can the Heltec board survive with these high temps ?

#10

You haven’t actually said what these high temps are. Just temps relative to your pain threshold.

Most off the shelf components can run to +85℃ which is way hotter than most people can stand.

But all components degrade quicker when heated.

And yours shouldn’t be getting hot to the touch.

You could look at the markings on the parts and identify them using a search engine.

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